Dual-circuit steer-by-wire steering system comprising a common cradle

ABSTRACT

The invention relates to a steer-by-wire steering system comprising a hydraulic control unit that acts on the steerable wheels ( 1, 20 ), the control unit having at least one cradle ( 4, 23 ), which is displaceably mounted on at least one guide rod ( 5, 24 ) that passes through the respective cradle ( 4, 23 ). The respective cradle ( 4, 23 ) and the corresponding guide rod(s) ( 5, 24 ) form working chambers (A 11 , A 12 , A 21 , A 22 ) of a piston-cylinder system, whereby each respective guide rod ( 5, 24 ) has at least one channel (KA 11 , KA 12 , KA 21 , KA 22 ), each terminating in the vicinity of a working chamber (A 11 , A 12 , A 21 , A 22 ). The cradle or cradles ( 4, 23 ) adjust the steerable wheels ( 1, 20 ) directly or by means of steering tie rods ( 2, 21 ).

The present invention relates to a steer-by-wire steering system,comprising a hydraulic control unit that acts on the steerable wheels.

The control units of generic dual-circuit steer-by-wire steering systemsnormally consist of two control cylinders, which are individuallymounted on their own and which need flexible feed lines to supply thefluid medium. Due to their structure the control cylinders are normallybulky and prone to fault on account of the flexible feed lines.

Object of the present invention is to create a steer-by-wire steeringsystem, the structure of which is as compact and as non-prone to faultas possible.

This object is achieved according to the invention with a steer-by-wiresteering system in accordance with the features of Claim 1. Furtheradvantageous configurations of the steer-by-wire steering system inaccordance with the invention arise as a result of the features of thesub-claims.

The steer-by-wire steering system in accordance with the invention isdistinguished in that as a result of fixed guide rods, which inparticular are secured directly to the vehicle bodywork or valve blocks,a large degree of flexural rigidity of the steering system is obtained,since the guide rods employed have a greater diameter in relation to thepiston rod used in conventional control cylinders. A cradle isdisplaceably mounted on the guide rods of the steer-by-wire steeringsystem in accordance with the invention, whereby the cradle as well asthe guide rods form working chambers of a piston-cylinder system. It iswithin the sense of the invention to use only one guide rod or howeveralso several guide rods for the steering system in accordance with theinvention. It is likewise within the sense of the invention that allguide rods form piston-cylinder systems with the cradle or cradles.However it is also possible that a minimum of one guide rod is provided,which only fulfills the cradle-guiding function, but does not form apiston-cylinder system.

Generally, the arrangement of the piston guide rods on the motor vehicleis arbitrary. Advantageously, the guide rods are arranged transversallyto the driving direction and parallel to the roadway. However, it isalso completely possible to arrange the guide rods in another directionon the vehicle.

If more than one guide rod is present, these are preferably arrangedparallel to each other at the same height. However, it is also possiblethat the guide rods are arranged one above the other and parallel toeach other. The point of application of force of the steering tie rodson the cradle(s), which is/are displaceably mounted on the guide rods,is to be selected as a function of the given installation space.Advantageously, the points of application of force of the steering tierods of both guided wheels are to be selected in such a way that theylie centrally between two parallel guide rods, so that no torque actsupon the guide rods. As a result of this central application of force itis in particular possible to provide long guide rods, whichadvantageously leads to minimum steering error when the springs arecompressed and released. One or more long guide rods can also be used,whereby in addition a central steering tie rod links the two points ofapplication of force of the two steering tie rods with one another. Thiscentral steering tie rod is to be arranged parallel to the guide rod(s).Advantageously, it is displaceably mounted on the bodywork parallel tothe guide rod(s), whereby advantageously no flexural stress acts uponthe steering tie rods.

Because the link with the vehicle framework occurs far on the outsidedue to the long guide rods, a more rigid connection of the guiderod-cradle system arises. Advantageously, the steer-by-wire steeringsystem in accordance with the invention has a modular construction.Thus, it is possible to place the guide rods between two valve blocks.Depending on the type of motor vehicle, the valve blocks and/or theguide rod-cradle system can be selected accordingly, whereby standardmodules can be used for different types of motor vehicle.

Because the guide rods themselves form the line for the fluid medium,advantageously no additional connecting hoses are necessary as in thecase of conventional steering systems, so that advantageously less riskof leakage results.

If two guide rods are used, each of which on their own form feed linesto working chambers of piston-cylinder systems, each guide rod is initself a component of a steering circuit, whereby the two steeringcircuits can be implemented purely as a dual-circuit or in addition, insome case as a mono-circuit, that is to say for example with a commonpump. In principle, the steer-by-wire steering system in accordance withthe invention can be wired similarly to all known steering circuitwiring. The two steering circuits, for example, can possess valveshaving open or closed center. However, it is also possible that asteering circuit is dimensioned as far as the level of force isconcerned, in such a way that it alone can apply the steering force whenthe motor vehicle is being driven in normal operation. The secondsteering circuit then serves as a reserve, which is activated either inthe event of failure of the first steering circuit or however ifnecessary, for example in parking and/or shunting operation, when highsteering force is necessary.

As already stated, if the above-described steer-by-wire steering systemis used in this way, the control valves fitted in the steering circuitscan be valves having open or closed center. The use of valves havingclosed center with simultaneous use of an accumulator has the advantagethat the pump does not have to be in continuous operation in order tobuild up a working pressure of the fluid medium, whereby advantageouslyenergy and thus fuel are saved.

As also already stated, the cradle in the case of the steer-by-wiresteering system in accordance with the invention can be configured bothwith tandem and single cylinders. In the case of the tandem cylinder,the working chambers of the piston-cylinder systems of each steeringcircuit are arranged beside each other in the axial direction and areseparated from one another by gaskets. If only one guide rod and onecradle and/or single cylinder is used, the working chambers of bothsteering circuits are arranged beside each other and/or one behind theother in the axial direction. Therefore a relatively small dimensionalsize results, whereby however the cradle and/or the control cylinder,which encompasses the guide rod from outside, is longer than the controlcylinders of the tandem system.

Embodiments of the steer-by-wire steering system in accordance with theinvention are described in detail below with reference to figures.

There is shown:

FIG. 1 a schematic illustration of a steer-by-wire steering system inaccordance with the invention;

FIG. 2 a dual-circuit steer-by-wire steering system with centrallyacting steering tie rods;

FIG. 3 a sectional view through a steer-by-wire steering system inaccordance with FIG. 2;

FIG. 4 a perspective view of a steer-by-wire steering system inaccordance with the invention;

FIG. 5 a view of the feed lines of the dual-circuit steer-by-wiresteering system in accordance with FIGS. 1 to 4;

FIG. 6 a detailed illustration of a steer-by-wire steering system inaccordance with the invention with only one guide rod;

FIG. 7 a cross sectional view through the piston-cylinder system of thesteer-by-wire steering system in accordance with FIG. 6.

FIG. 1 shows a schematic illustration of a first embodiment of thesteer-by-wire steering system in accordance with the invention, wherebya cradle 4, which is movably and/or displaceably mounted on two guiderods 5, adjusts steerable wheels 1 by means of steering arms 3 andsteering tie rods 2. The cradle 4 together with the guide rods 5 formsfour working chambers A₁₁, A₁₂, A₂₁, and A₂₂. The guide rods 5 arerigidly mounted on the bodywork or chassis of the vehicle between twovalve blocks 6. The cradle 4 and the guide rods 5 form a specialpiston-cylinder system in which the kinetics are reversed, since herethe piston and/or the guide rod(s) are static and the cylinder and/orcradle moves.

FIG. 2 shows a further embodiment of the steer-by-wire steering systemin accordance with the invention, in which the points of application offorce 2 a of the steering tie rods 2 are arranged on the cradle 4centrally between the two guide rods 5. As a result of the centralarrangement of the points of application of force 2 a to the guide rods5 minimum stress on the cradle 4 arises, as a result of which theconstruction of this embodiment does not need to be so substantial.

FIG. 3 shows a cross sectional view of the piston-cylinder system inaccordance with the embodiment of FIG. 2. The guide rods 5 ₁ and 5 ₂ aremounted between the valve blocks 6 ₁ and 6 ₂. The cradle 4 comprises twocylinders 4 a and 4 b, which are rigidly connected with one another bymeans of intermediate parts 4 c. The guide rods 5 ₁ and 5 ₂ are placedbetween the valve blocks 6 ₁ and 6 ₂. The free ends 5′₁ and 5″₁, 5′₂ and5″₂ are secured by means of fastening parts 6 a to the valve blocks 6 ₁and 6 ₂, in particular with their ends screwed into the valve blocks.The guide rods 5 ₁ and 5 ₂ are formed as tubes, which advantageouslyhave a circular cross section for outside and inside diameters. However,it is also possible to select any cross-sectional shape. Nevertheless,it is to be ensured here that a possible simple and durable seal must beguaranteed between the guide rods and the cradle. By selecting acircular cross section it is possible that the cavity of each cylinder 4a, 4 b can be produced for example by means of a borehole or however isformed by a simple tube. The guide rods 5 ₁ and 5 ₂ also have continuouscavities. The cavities can be realized by means of boreholes. However,it is equally possible to use a tube as a guide rod.

In each case, an inner tube 18 ₁, 18 ₂ is inserted from one end in thecavity of each guide rod 5 ₁, 5 ₂. The end 5″₁ and 5″₂ of each guide rod5 ₁, 5 ₂ is closed in each case by means of a seal D₁ and/or D₂, so thatthe medium flowing through the inner tube 18 ₁ and/or 18 ₂ inside theguide rod 5 ₁ and/or 5 ₂ into the respective working chamber A₁₂ and/orA₂₂ cannot escape from the guide rod 5 ₁ and/or 5 ₂ or from thepiston-cylinder system. The inner tubes 18 ₁ and/or 18 ₂ in each case ontheir end inside the cavity are encompassed by a seal D, which seals theinner tube 18 ₁ and/or 18 ₂ against the inner wall of the guide rod 5 ₁and/or 5 ₂ and thus divides the interior of the guide rods 5 ₁ and/or 5₂ into two sub-areas. The guide rod has window-like orifices 7, 8, 9 and10, which connect the feed and/or extraction lines with the workingchambers A₁₁, A₁₂, A₂₁ and A₂₂.

Should the cradle 4 be moved from left to right, a pressure can be builtup either in the working chamber A₁₁ or in the working chamber A₂₂.Thus, it is within the sense of the invention to apply fluid pressure toboth cylinders at the same time. Likewise, it is within the sense of theinvention, and this also applies for all embodiments illustrated, thatthe cylinder 4 a together with the guide rod 5 ₁ is a component of afirst steering circuit and the cylinder 4 b as well as the guide rod 5 ₂is a component of a second steering circuit. As already described, bothsteering circuits can operate in parallel. However, it is also possiblethat the first steering circuit is provided for normal driving and isdimensioned accordingly as far as its level of force is concerned,whereby the second steering circuit is only activated to assist thefirst steering circuit, for example during parking and/or shuntingoperation. If the first steering circuit should fail, the secondsteering circuit provides a fall back level, as a result of which thevehicle can continue to be steered safely.

FIG. 4 shows a perspective view of a steering system in accordance withthe invention with two guide rods 5 arranged in parallel, on which twocylinders are rigidly connected with one another by means ofintermediate parts 4 c, which together form a cradle 4. The guide rods 5are placed between two valve blocks 6. The valve blocks 6 correspond tothe valve blocks 6 ₁ and 6 ₂ schematically illustrated in FIG. 3.

With FIG. 5 once again the specific structure of the piston-cylindersystem is described, whereby the general structure corresponds to thatof FIG. 3, the difference being that the cylinders 4 are connecteddirectly, that is to say without intermediate elements (4 d). The guiderods 5 are formed as tubes, which are held parallel to each other bymeans of fastening parts 15, 16. The free ends 5″₁, 5″₂ are closed bymeans of screw plugs 12, 14 and inlaid gaskets 11, 13, so that no fluidmedium can escape at these ends. The screw plugs 12 and/or 14 press theguide rods 5 ₁ and 5 ₂ with their free ends 5′₁, 5′₂ into the respectivecylinder block. As a result, a sure and durable connection between theguide rods with their channels and the valve blocks results. It is,however, equally possible in an alternative embodiment to screw the ends5′₁ and 5′₂ of the guide rods with the valve blocks. The fluid medium ispumped through the opposite free ends of the guide rods 5 ₁ and 5 ₂ intothe channels KA₁₁ and KA₂₁ formed by the guide rods 5 ₁ and 5 ₂ towardsthe working chambers A₁₁ and A₂₁ and/or let out from these. The channelsKA₁₁ and KA₂₁ are formed by the inner wall of the guide rod 5 ₁ and/or 5₂ and the inner tube 18 ₁ and/or 18 ₂. The channels KA₁₁ and KA₂₁ areconnected via window-like orifices 8, 9 with the associated workingchambers A₁₁ and A₂₁. The channels KA₁₂ and KA₂₂ are formed by the innertubes 18 ₁ and/or 18 ₂. The channels KA₁₁ and KA₁₂ or KA₂₁ and KA₂₂ ineach case are sealed by a seal D, which encompasses or spans the finalarea of the inner tube 18 ₁ and/or 18 ₂ and lies against its outer walland at the same time against the inner wall of the guide rod 5 ₁ and/or5 ₂. The channels KA₁₂ and KA₂₂ are connected with the associatedworking chambers A₁₂ and A₂₂ via window-like orifices 7, 10. The ratiobetween inner diameter R_(i) of the guide rods 5 ₁ and/or 5 ₂ and outerdiameter R_(A) of the inner tubes 18 ₁ and/or 18 ₂ is to be dimensionedsuch that the flow cross-sections are roughly the same size or aresuitable for the respective demands. The cylinders 4 lie with their endareas 4 e, 4 f sealingly outwards on the guide rod 5 ₁ and/or 5 ₂, sothat no fluid medium can escape from the working chambers into theenvironment. The working chambers A₁₁ and A₁₂ or A₂₁ and A₂₂ of thefirst and second steering circuit in each case are separated from oneanother by a circular part K, which in particular can be molded in theshape of a collar outside on the guide rod 5 ₁ and/or 5 ₂. So that theinner tube 18 ₁ and/or 18 ₂ cannot be pushed too far into the guide rod5 ₁ and/or 5 ₂ stop elements S are to be provided. The stop elements Sin particular can be inserted or screwed into a window-like orificeand/or borehole of the guide rods 5 ₁ and/or 5 ₂.

FIG. 6 shows an alternative embodiment of a dual-circuit steer-by-wiresteering system in accordance with the invention, whereby only onesteered wheel 20 is illustrated, which can be moved by means of asteering tie rod 21, which is linked via the joint 21 a to a centralguide rod 26. The central guide rod 26 is rigidly connected with acradle 23, which in turn is displaceably mounted on a guide rod 24. Theguide rod 24 is mounted between two valve blocks 25, which are connectedwith the vehicle chassis 22. The central steering tie rod 26 isdisplaceably mounted parallel to the guide rod 24 by means of slidingbearings 27 on the chassis 22. As a result of the oblong arrangement ofthe cradle 23 the guide rod 24, which is smaller as far as its diameteris concerned, is relatively resistant to bending, so that the fasteningpoints of the guide rod 24 can be arranged relatively far on the outsideand therefore directly on the chassis 22.

FIG. 7 shows the piston-cylinder system in accordance with theembodiment of FIG. 6 in cross section. The guide rod 24 with its twoends lies in two valve blocks 40, whereby fluid medium can flow into thechannels KA₁₁, KA₁₂, KA₂₁ and KA₂₂ through the valve blocks 40 and/orflow out from these. Two inner tubes 28, and 282 are each inserted fromone end of the tube 24 into this and lie with their ends inserted in thetube 24 against stop elements 31, 32. The free ends of the inner tubes28 ₁ and 28 ₂ are encompassed by circular gaskets 35, 36, which liesealingly against the outer wall of the inner tubes 28 ₁, 28 ₂ and theinner wall of the tube 24. These gaskets separate the channels of onesteering circuit respectively from one another. The channels KA₁₂ andKA₂₂ are separated sealingly from one another by a gasket 39 inlaid inthe tube 24. The guide rod and/or the tube 24 have window-like orifices33, 34, 41 and 42, through which the channels KA₁₁, KA₁₂, KA₂₁ and KA₂₂are connected with the working chambers A₁₁, A₁₂, A₂₁ and A₂₂. Thedisplaceably mounted cylinder and/or cradle 25 encompasses the guide rodand/or the tube 24 and with this together forms the working chambers.The ends of the cylinder 25 are closed by means of gaskets 38, so thatno fluid medium can escape from the working chambers A₁₁ and A₂₁ intothe environment. The working chambers A₁₂ and A₂₂ are separated from oneanother by means of a collar 25 a and associated gasket 37 arranged onthe cylinder 25. The working chambers A₁₁ and A12 are separated from oneanother by a circular and/or collar-shaped part 29 and associatedgasket. For assembly, the part 29 can be pushed from the end onto thetube 24 and can be then connected captively with the tube 24. However,it is also possible to mold this collar-shaped part on the tube 24.Likewise, the working chambers A₂₁ and A₂₂ are separated from oneanother by means of a separating element 30 and associated gasket. Theseparating elements 29, 30 are rigidly fastened to the tube 24, whereasthe partition 25 a is displaced with the cylinder 25.

Of course it is possible that the parts forming the cylinders are notproduced integrally, for example from a tube and/or a cylinder, but areformed from two or several parts. Thus, it is possible, for example, toform the cylinder by means of two half shells, whereby gaskets are to beprovided between the two parts.

Generally, the connection of the channels formed by the guide rods andinner tubes on the fluid circuit of the respective steering circuits,can be configured arbitrarily. Of course, it is possible to deviate fromthe embodiments described specifically and yet make use of the inventiveidea. Thus, a guide rod can also be formed from two or several parts, ifthis is necessary for easier assembly. The individual parts forming aguide rod can for example be inserted into one another or screwedtogether or fastened or connected with one another in any other way. Thesame applies for the parts forming the cylinders and the cradle as awhole.

1-30. (canceled)
 31. A steer-by-wire system comprising: a hydrauliccontrol unit that acts on steerable wheels 1, wherein said control unithas at least one cradle which is adapted to adjust said steerable wheelsdirectly or via tie rods; at least one guide rod, wherein said at leastone cradle is displacebly mounted on said at least one guide rod, whichin particular passes through a respective one of said cradles, whereinsaid at least one cradle together with said at least one pertainingguide rod, form working chambers of a piston-cylinder system, whereinsaid at least one guide rod is a tube and has at least one channel whichrespectively ends in a vicinity of one of said working chambers, whereina first channel is formed by said tube itself; and an inner tubedisposed in said first channel, wherein said inner tube has an outerdiameter that is less than an inner diameter of said first channel, andwherein said inner tube forms a second channel.
 32. A steer-by-wiresteering system according to claim 31, wherein a plurality of cradlesare provided that are rigidly connected with one another directly or bymeans of at least one intermediate part and form a single cradle.
 33. Asteer-by-wire steering system according to claim 31, wherein a given oneof said at least one guide rod is provided with a plurality of channelsthat extend from one or both end faces or regions of said guide rod intosaid guide rod.
 34. A steer-by-wire steering system according to claim31, wherein said at least one guide rod is secured or mounted on avehicle chassis directly or by means of intermediate parts.
 35. Asteer-by-wire steering system according to claim 31, wherein said atleast one guide rod is disposed between two valve blocks and wherein atleast one of said channels and feed lines of said at least one guide rodare in operative communication with valves of at least one of said valveblocks.
 36. A steer-by-wire steering system according to claim 31,wherein a guide rod that together with a carriage form working chambersis provided with at least one outwardly directed collar that inparticular is formed thereon, wherein a given collar respectivelyseparates two working chambers from one another.
 37. A steer-by-wiresteering system according to claim 35, wherein two guide rods aredisposed parallel to one another between two valve blocks and passthrough a cradle wherein respective channels of said two guide rods arerespectively in operative communication with only one valve block,wherein said cradle with each guide rod, forms working chambers of apiston-cylinder system, and wherein each guide rod, together with theworking chambers formed thereby and the associated valve block, form aseparate steering circuit.
 38. A steer-by-wire steering system accordingto claim 37, wherein a respective guide rod is surrounded by a cylinderend faces of which respectively rest in a sealing manner againstpertaining ones of said guide rods, and wherein two cylinders areprovided and are interconnected directly or via at least one connectionpart and form said cradle.
 39. A steer-by-wire steering system accordingto claim 37, wherein points of application of force or mountinglocations of said tie rods are disposed between said two guide rods inparticular being centrally disposed relative to said guide rods.
 40. Asteer-by-wire steering system according to claim 37, wherein points ofapplication of force or mounting locations of said tie rods are disposedadjacent to said two guide rods.
 41. A steer-by-wire steering systemaccording to claim 37, wherein said at least one guide rod is a tubehaving an inner diameter that forms said first channel and in aninterior of which is disposed said inner tube having an outer diameterthat forms said second channel, wherein both of said channels areoperatively connected with the same valve block, and wherein a gasketsealingly engages about a surface of said inner tube in a vicinity of afree end thereof and sealingly rests against an inner wall of said firstchannel of said guide rod.
 42. A steer-by-wire steering system accordingto claim 41, wherein said gasket separates said first and secondchannels from one another and divides an interior of said guide rod intotwo regions.
 43. A steer-by-wire steering system according to claim 42,wherein at least one window-like orifice is disposed in each wall ofsaid guide rod and respectively connects a region with a workingchamber.
 44. A steer-by-wire steering system according to claim 42,wherein in a vicinity of -said gasket said guide rod is provided with aperipheral, collar-shaped projection that separates the working chambersfrom one another.
 45. A steer-by-wire steering system according to claim31, wherein a guide rod formed by an outer tube passes through saidcradle wherein disposed in said outer tube are two inner tubes thatrespectively extend from an end face into said outer tube, wherein agasket divides an interior of said outer tube into two partial chambersthat are separated from one another, and a respective annular gasketwhich is disposed between an inner tube and said outer tube, seals thetwo channels formed by said outer tube and said inner tube from oneanother, and wherein said outer tube is provided with window-likeorifices that connect the channels with the working chambers that areformed by said outer tube and said cradle.
 46. A steer-by-wire steeringsystem according to claim 45, wherein said cradle is provided with atubular part through which said outer tube passes, and wherein gasketsdisposed between said tubular part and said outer tube seal the workingchambers toward the outside.
 47. A steer-by-wire steering systemaccording to claim 45, wherein a respective collar which is disposed onsaid outer tube and is directed outwardly, separates said workingchambers of a steering circuit from one another.
 48. A steer-by-wiresteering system according to claim 47, wherein said collar is formed onsaid outer tube or is formed by an additional annular part that isconnected with said outer tube.
 49. A steer-by-wire steering systemaccording to claim 45, wherein an annular gasket and an inwardlydirectly collar that is disposed on a tubular portion of said cradle,separate two adjacent working chambers of two steering circuits from oneanother.
 50. A steer-by-wire steering system according to claim 31,wherein an end of respective ones of said tie rods are rotatably mountedon said cradle.
 51. A steer-by-wire steering system according to claim31, wherein a central tie rod is disposed parallel to said cradle and issecured thereto or integrated therewith, wherein said central tie rod isdisplaceably mounted on a vehicle chassis parallel to said cradle, andwherein an end of respective ones of said tie rods are rotatably orpivotably mounted on said central tie rod.
 52. A steer-by-wire steeringsystem according to claim 31, wherein two steering circuits operate inparallel at the same time, and in particular an associated control valveis a valve having open center or closed center.
 53. A steer-by-wiresteering system according to claim 31, wherein a level of force of afirst steering circuit is dimensioned such that, with the exception of aparking or shunting operation of a vehicle being steered, appliessufficiently large forces for a normal driving operation.
 54. Asteer-by-wire steering system according to claim 31, wherein a secondsteering circuit takes over the function of the first steering circuitupon failure of said first steering circuit.
 55. A steer-by-wiresteering system according to claim 54, wherein a control valve of saidfirst steering circuit is a valve having open center, and a controlvalve of said second steering circuit is a valve having closed center.56. A steer-by-wire steering system according to claim 52, wherein asecond steering circuit has a level of force that is the same or lessthan that of a first steering circuit.
 57. A steer-by-wire steeringsystem according to claim 31, wherein said steering system is providedwith additional guides for a mounting of said at least one cradle.
 58. Asteer-by-wire steering system according to claim 57, wherein at leastone additional guide is a guide rod that passes through said cradle.